<!DOCTYPE html>
<html>
<body>
<table style="width: 6em; background: yellow">
    <tr>
        <td id="big">mmmmmmmmmmmmmmmm</td>
    </tr>
</table>
<script>
  document.body.offsetWidth;
  var big = document.getElementById("big");
  var r = big.firstChild.splitText(8);
  big.insertBefore(document.createElement("WBR"), r);
</script>
</body>
</html>
